Vehicle seat with load sensor and pan frame including inclined edge

ABSTRACT

A passenger□s weight measurement device for a vehicle seat includes an upper rail provided on a lower rail that is fixable to a vehicle floor, the upper rail being movable in at least one of rear and front directions; a load sensor fixed onto the upper rail; and a frame provided on the load sensor and below the vehicle seat. In plan view, the load sensor protrudes from the frame in at least one of left and right directions.

This is Continuation of U.S. application Ser. No. 16/157,379 filed onOct. 11, 2018, which is a continuation of U.S. application Ser. No.14/842,185 filed on Sep. 1, 2015, which is a continuation of U.S.application Ser. No. 13/836,773 filed Mar. 15, 2013, which is aContinuation of U.S. application Ser. No. 13/137,713 filed Sep. 7, 2011,which is a Continuation of U.S. application Ser. No. 12/875,594 filedSep. 3, 2010, which is a Continuation of U.S. application Ser. No.11/992,548 filed Mar. 25, 2008, which is a National Stage ofInternational Application No. PCT/JP2006/319477 filed Sep. 29, 2006,which in turn claims the benefit of priority from Japanese ApplicationNo. 2005-286881 filed Sep. 30, 2005. The disclosures of the priorapplications are hereby incorporated by reference herein in theirentirety.

TECHNICAL FIELD

The present invention relates to a passenger's weight measurement devicefor a vehicle seat, which measures a weight of a passenger seated on thevehicle seat, and to an attachment structure for attaching a load sensorto the passenger's weight measurement device.

BACKGROUND ART

In recent years, in some cases, operations of various safety devicessuch as a seat belt and an air bag have been controlled in accordancewith a weight of a passenger seated on a vehicle seat for the purpose ofenhancing performance of the safety devices. In a conventionalpassenger's weight measurement device that measures the weight of theseated passenger, a load sensor is interposed between a vehicle floorand the vehicle seat (for example, refer to Patent Document 1 and PatentDocument 2).

Patent Document 1: JP A H8-164039

Patent Document 2: JP A H9-207638

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, there is a dimension error or an assembling position error whenthe passenger's weight measurement device is assembled, when the vehicleseat is fixed to the passenger's weight measurement device or when thepassenger's weight measurement device is fixed to the vehicle floor, orthe like. Accordingly, it has been difficult to assemble the passenger'sweight measurement device.

In this connection, it is an object of the present invention to providea passenger's weight measurement device for a vehicle seat, which ismore easily assembled, and to provide an attachment structure for a loadsensor.

Means for Solving the Problems

In order to solve the above-described problem, a passenger's weightmeasurement device for a vehicle seat according to the present inventioncomprises: an upper rail provided on a lower rail fixed to a vehiclefloor so as to be movable in a rear and front direction; a load sensorfixed onto the upper rail; and a frame provided on the load sensor andbelow the vehicle seat, wherein a rod is extended from the load sensor,the rod sequentially penetrates the frame and a spring holder and isinserted into a coil spring, a nut is screwed to the rod from above thespring holder, and the coil spring is sandwiched between the springholder and the frame and is compressed by tightening the nut to thespring holder.

An attachment structure for a load sensor according to the presentinvention is an attachment structure for attaching the load sensor to aframe provided below a vehicle seat, wherein a rod is extended from theload sensor, the rod sequentially penetrates the frame and a springholder and is inserted into a coil spring, a nut is screwed to the rodfrom above the spring holder, and the coil spring is sandwiched betweenthe spring holder and the frame and is compressed by tightening the nutto the spring holder.

In the present invention, preferably, the spring holder includes a cupportion in which a through hole through which the rod penetrates isformed in a bottom, and a flange formed on an outer circumference of thecup portion, and the cup portion is inserted through the coil spring,the nut is inserted into the cup portion to tighten the bottom of thecup portion, and the coil spring is sandwiched between the flange andthe flame.

In the present invention, preferably, a collar through which the rod isinserted penetrates the frame, the spring holder is sandwiched betweenthe collar and the nut, and the coil spring and the collar aresandwiched between the nut and the load sensor.

In accordance with the present invention, the nut is screwed to the rodfrom above the spring holder, and the coil spring is sandwiched betweenthe spring holder and the frame by tightening the nut. Accordingly, theframe can be shifted in the vertical direction with respect to the loadsensor.

Effect of the Invention

In accordance with the present invention, the frame can be shifted inthe vertical direction with respect to the load sensor. Accordingly,even if the lower rail, the upper rail, the frame and the like aredistorted during the assembling or the like, an initial load generatedby such distortions can be prevented from being applied to the loadsensor.

Moreover, the coil spring is sandwiched between the frame and the springholder in a state of being compressed by tightening the nut.Accordingly, the load sensor is fixed to the frame more stably andappropriately. Therefore, it becomes easier to assemble the passenger'sweight measurement device.

Furthermore, the load is stably applied from the coil spring to the nutowing to elastic deformation of the coil spring, which is caused bytightening the nut.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 This is a perspective diagram of a passenger's weight measurementdevice 1 for a vehicle seat.

FIG. 2 This is an exploded perspective diagram of the passenger's weightmeasurement device 1.

FIG. 3 This is a perspective diagram of a load sensor 21.

FIG. 4 This is a plan diagram of a rectangular frame 30.

FIG. 5 This is a plan diagram of a right front portion of therectangular frame 30.

FIG. 6 This is a cross-sectional diagram showing a cross section along asection line VI-VI of FIG. 5.

FIG. 7 This is a cross-sectional diagram showing a cross section along asection line VII-VII of FIG. 5.

FIG. 8 This is a cross-sectional diagram showing a modification exampleof FIG. 6, and showing a cross section along the section line VI-VI in asimilar way to FIG. 6.

FIG. 9 This is a cross-sectional diagram showing a modification exampleof FIG. 7, and showing a cross section along the section line VII-VII ina similar way to FIG. 7.

BEST MODE FOR CARRYING OUT THE INVENTION

A best mode for carrying out the present invention will be describedbelow by using the drawings. On embodiments to be described below, avariety of technically preferable limitations are imposed in order tocarry out the present invention; however, the scope of the invention isnot limited to the following embodiments and illustrated examples.

FIG. 1 is a perspective diagram of a passenger's weight measurementdevice 1 for a vehicle seat, and FIG. 2 is an exploded perspectivediagram of the passenger's weight measurement device 1.

As shown in FIG. 1 and FIG. 2, a slide adjuster 2 for adjusting aback-and-forth position of the vehicle seat is attached onto a floor ofa passenger's room. The slide adjuster 2 includes a left and right pairof lower rails 3 provided in parallel to each other, a left and rightpair of upper rails 4 engaged with the lower rails 3 so as to be capableof sliding on the respective lower rails 3 in a rear and front directionwith respect to the lower rails 3, a lower bracket 5 fixed to lowersurfaces of the lower rails 3 by bolt/nut coupling or rivet coupling andbridged between the left and right lower rails 3, a lock mechanism 6 forlocking the upper rails 4 to the lower rails 3 and for releasing thelocking, brackets 7 attached onto front end portions of the lowersurfaces of the respective lower rails 3, and brackets 8 attached ontorear end portions of the lower surfaces of the respective lower rails 3.These brackets 7 and 8 are attached onto the vehicle floor, and thelower rails 3 are fixed to the vehicle floor.

Brackets 9 are fixed to middle positions of upper surfaces of therespective upper rails 4 in a rear and front direction by the bolt/nutcoupling or the rivet coupling. The brackets 9 are provided in a stateof being erected with respect to upper surfaces of the upper rails 4. Aright end portion of a submarine pipe 10 is welded to the brackets 9,and the submarine pipe 10 is bridged between the two left and rightbrackets 9.

A load sensor 21 is mounted on a front end portion of the upper surfaceof the right upper rail 4, and another load sensor 21 is mounted on arear end portion thereof. Also on the upper surface of the left upperrail 4, load sensors 21 are mounted on a front end portion and rear endportion thereof, respectively. When viewed from the above, these fourload sensors 21 are arranged so as to be apexes of a square or arectangle.

FIG. 3 is a perspective diagram of the load sensor 21. All of the loadsensors 21 are provided in a similar way. As shown in FIG. 3, the loadsensor 21 includes a columnar sensing portion 21 a that senses a load, aplate-like flange portion 21 b extending horizontally in a rear andfront direction from a lower end of the sensing portion 21 a, a rod 21 cextending upward from an upper end of the sensing portion 21 a, and aconnector 21 d extending from the sensing portion 21 a so as to beparallel to the flange portion 21 b. The rod 21 c is formed into a malescrew shape. Female screw-shaped circular holes 21 e and 21 f whichpenetrate the flange portion 21 b in the vertical direction are formedin front and rear portions of the flange portion 21 b, respectively. Thesensing portion 21 a incorporates a strain gauge therein, and the loadis converted into an electric signal by the strain gauge.

As shown in FIG. 2, the load sensor 21 is fixed to the right upper rail4. Specifically, a lower surface of the flange portion 21 b abuts on theupper surface of the upper rail 4, and two bolts 22 inserted through theupper rail 4 upward from below are screwed to the circular holes 21 eand 21 f, respectively. Therefore, the load sensor 21 is fixed. Notethat the load sensor 21 may be fixed to the upper rail 4 by fasteningnuts to the bolts 22 on the flange portion 21 b without forming anyscrew threads in the circular holes 21 e and 21 f.

Any load sensor 21 is fixed to the upper rails 4 as described above.However, with regard to the two load sensors 21 fixed to the rearportions thereof, the connectors 21 d are directed forward, and withregard to the two load sensors 21 fixed to the front portions thereof,the connectors 21 d are directed backward.

As shown in FIG. 1 and FIG. 2, the frame 30 having a rectangular frameshape is mounted on these four load sensors 21. FIG. 4 is a top diagramof the rectangular frame 30. As shown in FIG. 4, the rectangular frame30 is composed of a left and right pair of beams 31, a front beam 32,and a rear cross pipe 33.

Either of the beams 31 is a metal member having a U-shaped crosssection, and has a web 31 a, an inner flange 31 b, and an outer flange31 c. Attachment holes 31 d are formed in a front portion and a rearportion of the web 31 a, respectively.

The front beam 32 is a metal member having a U-shaped cross section, andhas a web 32 a, a front flange 32 b, and a rear flange 32 c. The frontbeam 32 is bridged between front end portions of the left and rightbeams 31, and is welded to these beams 31.

The cross pipe 33 is bridged between rear end portions of the left andright beams 31, and is welded to these beams 31.

The rods 21 c of the load sensors 21 are inserted into the respectiveattachment holes 21 d upward from below, and nuts 46 are screwed to therods 21 c. Therefore, the load sensors 21 are attached onto a rightfront portion, a right rear portion, a left front portion and a leftrear portion of the rectangular frame 30, respectively. Referring toFIG. 5 to FIG. 7, an attachment structure for attaching the right frontload sensor 21 onto the right front portion of the rectangular frame 30will be described. FIG. 5 is a plan diagram of the right front portionof the rectangular frame 30, FIG. 6 is a cross-sectional diagram showinga cross section along a line VI-VI, and FIG. 7 is a cross-sectionaldiagram showing a cross section along a line VII-VII. As shown in FIG. 5to FIG. 7, an annular bush 41 is fitted to an edge of the right frontattachment hole 31 d, and grease is applied on the bush 41. The bush 41is an oilless bush formed by impregnating oil into a metal material, oris made of synthetic resin. The bush 41 may be one made of othermaterials. Moreover, a stepped collar 42 composed of a cylindricalportion 42 a and an annular plate-like flange portion 42 b formed on oneend surface of the cylindrical portion 42 a is inserted through theattachment hole 31 d in an inside of the bush 41. Here, the cylindricalportion 42 a is inserted through the attachment hole 31 d upward frombelow, and the flange portion 42 b engages with a lower surface of theweb 31 a via the bush 41. Therefore, the stepped collar 42 is not pulledout upward. Moreover, the cylindrical portion 42 a protrudes from anupper surface of the web 31 a, and an upper end surface of thecylindrical portion 42 a is located at a higher position than the uppersurface of the web 31 a. Here, the cylindrical portion 42 a is fitted tothe bush 41, and there is no gap between the cylindrical portion 42 aand the bush 41.

The rod 21 c of the load sensor 21 is inserted through the steppedcollar 42 upward from below. An inner diameter of the stepped collar 42is designed to be slightly larger than a diameter of the rod 21 c, andby such designing, a dimension error and an attachment position errorare solved.

The nut 46 is screwed to the rod 21 c. A plain washer 43, a coil spring44 and a spring holder 45 are interposed between the upper surface ofthe web 31 a of the beam 31 and the nut 46. The rod 21 c and thecylindrical portion 42 a of the stepped collar 42 are inserted throughthe plain washer 43, and the plain washer 43 is set in a state of beingmounted on the web 31 a, and particularly, on the bush 41. Furthermore,the rod 21 c is inserted through the coil spring 44, and the coil spring44 is set in a state of being mounted on the plain washer 43. A portionof the coil spring 44, which is brought into contact with the plainwasher 43, is formed to be flat.

The spring holder 45 includes a cup portion 45 c in which a through holeis formed in a bottom 45 b, and an annular flange 45 a formed on anouter circumferential surface in an opening of the cup portion 45 c.Then, the rod 21 c penetrates through the through hole of the bottom 45b of the cup portion 45 c, the bottom 45 b of the cup portion 45 c isset in a state of being mounted on an end surface of the stepped collar42, and the cup portion 45 c is inserted into the coil spring 44.Moreover, the coil spring 44 and the plain washer 43 are set in a stateof being sandwiched between the flange 45 a of the spring holder 45 andthe web 31 a.

The nut 46 is screwed to the rod 21 c in a state of being inserted intothe cup portion 45 c, and by tightening the nut 46, the bottom 45 b ofthe cup portion 45 c is sandwiched between the nut 46 and the upper endsurface of the cylindrical portion 42 a, and the coil spring 44 and theplain washer 43 are sandwiched between the flange 45 a and the web 31 aof the beam 31. Moreover, since the coil spring 44 is compressed bytightening the nut 46, the load is applied to the nut 46, andaccordingly, the nut 46 is prevented from being loosened. Note that thecoil spring 44 is set in a state of being mounted on the web 31 a of thebeam 31 via the plain washer 43. However, the coil spring 44 may be setin a state of being directly mounted on the web 31 a of the beam 31, andthe coil spring 44 may be sandwiched between the flange 45 a and the web31 a.

Like the right front load sensor 21, the left front, left rear and rightrear load sensors 21 are attached onto the left front, left rear andright rear attachment holes 31 d, respectively. In a state where thefour load sensors 21 are attached onto the rectangular frame 30, thesubmarine pipe 10 is located behind the front beam 32.

As shown in FIG. 1 and FIG. 2, side frames 51 are welded to the outerflanges 31 c of the left and right beams 31, respectively. These sideframes 51 are parts of a bottom frame of the vehicle seat. Each sideframe 51 may include a narrow portion 51 a, front and rear protrusions51 b and 51 c, and a hole 51 d between those protrusions.

From above, front portions of the side frames 51 are covered with a panframe 53, and the side frames 51 and the pan frame 53 are fixed to eachother by the bolt/nut coupling or the rivet coupling. The pan frame 53may include an inclined edge 53 a that is inclined rearwardly and ahollow 53 b. A seat spring 54 is bridged between the cross pipe 33 andthe pan frame 53, a cushion is mounted on the pan frame 53 and the seatspring 54, and the cushion, the pan frame 53 and the side frames 51 areentirely covered with a cover.

A backrest frame is coupled to rear ends of the side frames 51, and iscapable of rising and falling by a reclining mechanism. Note that thebackrest frame and the cushion are not shown in order to make it easy toview the drawings.

In the passenger's weight measurement device 1 configured as describedabove, when a passenger is seated on a seat bottom, a weight of thepassenger is applied to the four load sensors 21 through the rectangularframe 30, and is converted into electric signals by these load sensors21.

Here, the load sensors 21 are attached between the upper rails 4 and therectangular frame 30, and the load sensors 21 move in a rear and frontdirection integrally with the vehicle seat. Accordingly, a load inputtedfrom the vehicle seat to the load sensors 21 can be always kept constantirrespective of position of the vehicle seat in a rear and frontdirection. Therefore, measuring accuracy of the passenger's weight canbe enhanced.

Moreover, the spring holder 45 is mounted on the upper end surface ofthe stepped collar 42, and the coil spring 44 is sandwiched between thespring holder 45 and the web 31 a by tightening the nut 46. Accordingly,the rectangular frame 30 can be shifted in the vertical direction withrespect to the load sensors 21. Therefore, noise of the load generatedby distortion of the slide adjuster 2 and the like becomes smaller.

Moreover, even if the rectangular frame 30 can be shifted in thevertical direction with respect to the load sensors 21, the coil springs44 are interposed between the nuts 46 and the webs 31 a, andaccordingly, the load sensors 21 can be fixed to the rectangular frame30 more stably and appropriately. Therefore, it becomes easier toassemble the passenger's weight measurement device 1.

Moreover, the load is stably applied from each of the coil springs 44 toeach of the nuts 46 owing to elastic deformation of the coil spring 44,which is caused by tightening the nut 46.

Moreover, the submarine pipe 10 is located behind the front beam 32, andaccordingly, when forward inertial force is applied to the passengerowing to a frontal collision or the like of the vehicle, buttocks of thepassenger seated on the vehicle seat are restrained by the submarinepipe 10. Therefore, a so-called submarine phenomenon in which thepassenger moves under a waist belt can be prevented.

Note that the present invention is not limited to the above-describedembodiment, and various improvements and design changes can be madewithin the scope without departing from the gist of the presentinvention.

In the above-described embodiment, the coil spring 44 is set in thestate of being mounted on the plain washer 43, and the portion of thecoil spring 44, which is brought into contact with the plain washer 43,is made flat. However, for example as shown in FIG. 8 and FIG. 9, awasher 431 in which an inner portion thereof is formed as a protrudingportion 431 a protruding upward, may be used. An outer edge portion ofthe protruding portion 431 a is formed into a curved surface, and a stepdifference 431 b formed by the protruding portion 431 a is formed on anupper surface of the washer 431. An end portion of the coil spring 44 isset in a state of being engaged with the step difference 431 b, and thecoil spring 44 abuts on the curved surface of the protruding portion 431a and a flat surface of the washer 431. Therefore, the coil spring 44 iscentered by the protruding portion 431 a of the washer 431 so as not toslip on the flat surface of the washer 431.

What is claimed is:
 1. A vehicle seat with a load sensor, the vehicleseat comprising: a first load sensor; a frame which is provided on thefirst load sensor and which includes: left and right longitudinalmembers that each extend in front and rear directions; a pan framebridged between front portions of the longitudinal members; a submarinepipe which extends in left and right directions and which is lower thanthe pan frame; and left and right brackets that respectively supportleft and right ends of the submarine pipe, wherein the pan frameincludes an inclined edge on at least one of left and right sides of thepan frame, the inclined edge being inclined rearward, the first loadsensor is rearward of the inclined edge of the pan frame, the bracketsare inclined relative to a vertical direction, and the first load sensoris rearward of the brackets.
 2. The vehicle seat with the load sensoraccording to claim 1, wherein the pan frame includes a hollow on a frontside of the pan frame, the hollow being indented downward, the inclinededge of the pan frame is rearward of the hollow, and the brackets arerearward of the hollow.
 3. The vehicle seat with the load sensoraccording to claim 2, further comprising: a second load sensor in frontof the first load sensor, wherein the first load sensor and the secondload sensor respectively include a first connector and a secondconnector which face each other rearward of the hollow.
 4. The vehicleseat with the load sensor according to claim 1, further comprising: across pipe bridged between rear portions of the longitudinal members,wherein the longitudinal members each include a narrow portion rearwardof the inclined edge of the pan frame, the narrow portion being narrowerthan another portion of the longitudinal member, and the first loadsensor is rearward of a front end of a said narrow portion.
 5. Thevehicle seat with the load sensor according to claim 1, wherein thefirst load sensor includes a connector, at least one of the longitudinalmembers comprises a protrusion that expands outward, and a length of theprotrusion in the front and rear directions is larger than a width ofthe connector of the first load sensor in left and right directions. 6.The vehicle seat with the load sensor according to claim 5, wherein theframe further includes a cross pipe bridged between rear portions of thelongitudinal members, and rearward of the connector of the first loadsensor and the protrusion, the cross pipe penetrates the longitudinalmembers.
 7. The vehicle seat with the load sensor according to claim 1,further comprising: a second load sensor, wherein each of the first loadsensor and the second load sensor includes a connector, and at least oneof the longitudinal members comprises: two protrusions that expandoutward respectively around the first load sensor and the second loadsensor; and a hole between the two protrusions.
 8. The vehicle seat withthe load sensor according to claim 1, further comprising: left and rightrails that comprise: left and right lower rails fixed to a vehiclefloor; and left and right upper rails provided on the left and rightlower rails so as to be movable in the front and rear directions; and asecond load sensor in front of the brackets, wherein the first loadsensor, the second load sensor, and the brackets are fixed onto theupper rails.
 9. The vehicle seat with the load sensor according to claim1, further comprising: left and right rails that comprise: left andright lower rails fixed to a vehicle floor; and left and right upperrails provided on the left and right lower rails so as to be movable inthe front and rear directions; a second load sensor; and a lockmechanism for locking the upper rails to the lower rails and forreleasing the locking, wherein a center of the lock mechanism in theleft and right directions protrudes forward to be in front of the secondload sensor.
 10. A method of manufacturing a vehicle seat with a loadsensor, the method comprising: fixing left and right rails to a vehiclefloor; fixing left and right brackets that respectively support left andright ends of a submarine pipe to the left and right rails so as to beinclined relative to a vertical direction, the submarine pipe extendingin left and right directions; fixing a first load sensor rearward of thebrackets on one of the left and right rails; and providing a frame onthe first load sensor, wherein the frame comprises: left and rightlongitudinal members that each extend in front and rear directions; anda pan frame bridged between front portions of the longitudinal members,and the pan frame includes an inclined edge on at least one of left andright sides of the pan frame, the inclined edge being inclined rearwardand being in front of the first load sensor.
 11. The method ofmanufacturing the vehicle seat with the load sensor according to claim10, wherein the pan frame includes a hollow on a front side of the panframe, the hollow being indented downward, the inclined edge of the panframe is rearward of the hollow, and the brackets are behind the hollow.12. The method of manufacturing the vehicle seat with the load sensoraccording to claim 10, the method further comprising: fixing a secondload sensor in front of the first load sensor on one of the left andright rails, wherein the first load sensor and the second load sensorrespectively include a first connector and a second connector which faceeach other rearward of the hollow.
 13. The method of manufacturing thevehicle seat with the load sensor according to claim 10, wherein theframe further comprises a cross pipe bridged between rear portions ofthe longitudinal members, the longitudinal members each include a narrowportion rearward of the inclined edge of the pan frame, the narrowportion being narrower than another portion of the longitudinal member,and the frame is provided on the first load sensor such that the firstload sensor is rearward of a front end of a said narrow portion.
 14. Themethod of manufacturing the vehicle seat with the load sensor accordingto claim 10, wherein the first load sensor includes a connector, atleast one of the longitudinal members comprises a protrusion thatexpands outward, and a length of the protrusion in the front and reardirections is larger than a width of the connector of the first loadsensor in the left and right directions.
 15. The method of manufacturingthe vehicle seat with the load sensor according to claim 14, wherein theframe further includes a cross pipe bridged between rear portions of thelongitudinal members, and rearward of the connector of the first loadsensor and the protrusion, the cross pipe penetrates the longitudinalmembers.
 16. The method of manufacturing the vehicle seat with the loadsensor according to claim 10, the method further comprising: fixing asecond load sensor on one of the left and right rails; wherein each ofthe first load sensor and the second load sensor includes a connector,and at least one of the longitudinal members comprises: two protrusionsthat expand outward respectively around the first load sensor and thesecond load sensor; and a hole between the two protrusions.
 17. Themethod of manufacturing the vehicle seat with the load sensor accordingto claim 10, the method further comprising: fixing a second load sensorin front of the brackets on one of the left and right rails, wherein theleft and right rails comprise: left and right lower rails fixed to thevehicle floor; and left and right upper rails provided on the left andright lower rails so as to be movable in the front and rear directions,and the first load sensor, the second load sensor, and the brackets arefixed onto the upper rails.
 18. The method of manufacturing the vehicleseat with the load sensor according to claim 10, the method furthercomprising: fixing a second load sensor on one of the left and rightrails; and fixing a lock mechanism on the left and right rails, whereinthe left and right rails comprise: left and right lower rails fixed tothe vehicle floor; and left and right upper rails provided on the leftand right lower rails so as to be movable in the front and reardirections, the lock mechanism is for locking the upper rails to thelower rails and for releasing the locking, and a center of the lockmechanism in the left and right directions protrudes forward to be infront of the second load sensor.